The present invention relates to injection molding devices and more particularly to an injection molding apparatus having features as adapted to the deformation caused by heat, closed loop of force, isolation of deformation, and modular design.
A conventional injection molding process comprises the steps of feeding a heated liquid (e.g., magnesium, aluminum, zinc alloy, or thermoplastic substances having a temperature over 300xc2x0 C.) from supply means to barrel, blending and conveying the material forward through the rotating screw, controlling the volume of material and injecting the same into a die cavity when pressure of material builds up to a predetermined value, and cooling and setting. In view of the foregoing, liquid is always kept at a high temperature environment between the supplying and injecting phases.
A conventional injection molding apparatus is illustrated in FIG. 1 wherein a high temperature is maintained from the section of supply means 12b and throat portion 12c to barrel 12a for uniformly feeding material. It is found that heat is transferred to base 10a and links 11a by conduction. As such, the apparatus may be deformed by heat, which in turn causes a parallel deviation between links 11a, thus deteriorating the injection performance.
For example, in an injection molding apparatus for magnesium alloy, molten magnesium alloy has a flow temperature about 580xc2x0 C. Also, barrel 12a is kept at above 650xc2x0 C. due to the above heat convection effect. As such, base 10a and each link 11a have 225xc2x0 C. and 168xc2x0 C. temperature rises, respectively, due to heat transferred from barrel 12a to base 10a and links 11a. As such, a parallel deviation between links 11a connected to base 10a is generated. In an experiment data, deviation in one link 11a is more than 0.16 mm in the horizontal direction and more than 0.06 mm in the vertical direction, respectively. As a result, performance of the apparatus and precision of products both deteriorate significantly.
It is thus an object of the present invention to provide an injection molding apparatus comprising a barrel for conveying molten substances, a screw, a first base for supporting the barrel, a power unit, a second base for supporting the power unit, a plurality of links, a screw driving means, a plurality of injection guide links, and an injection connecting plate wherein the first base is threadedly secured to the bed. Further, a potential lengthening of links caused by injection is avoided by the slidingly movable second base on the rail of the bed. As such, deformation of bases caused by connected links during operation is prevented. Also, the fastening zone of the first base is coincident in the centerline of the barrel. As such, any deformation in the barrel caused by heat is uniformly distributed to either side of the centerline. Thus, an uneven deformation of bases is avoided, thereby maintaining the centerlines of screw and barrel substantially coincident. This apparatus can manufacture high precision products.
It is another object of the present invention to provide an injection molding apparatus wherein the force generated by the power unit during injection is transmitted through the injection connecting plate, injection guide links, screw driving means, screw, barrel, first base, links, second base, and back to the power unit to form a closed loop without passing through the bed. As such the bed only provides a support for the apparatus without additional force and torque being exerted thereon. This greatly decreases the reliance of components of the apparatus on bed during injection.
It is still another object of the present invention to provide an injection molding apparatus wherein the links simply act as transmitting injection force such that any potential deformation thereof caused by heat is minimized. This apparatus is particularly suitable to high speed injection molding with the linear moving speed of the rotating screw over two meters per second (2 m/s).
It is still another object of the present invention to provide an injection molding apparatus wherein the first base is the most important component such that the designs and geometry of all other components are conformed to the first base rather than the bed. As a result, no positioning device and associated geometry precision is required in the bed. This greatly simplifies assembly of the apparatus.
The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.